I hope they pass, and try to plot for them passing but I feel like I need a swoop-and-save always in the wings.
Ah, here we clearly have part of the problem. They're in a situation where they would fail most of the time if you weren't engineering things for them to succeed, so they should fail some or most of the time. If you feel bad for railroading them or for removing the challenge from the game by ensuring that they don't fail, stop doing that.
PCs don't need to succeed all the time, especially when the danger isn't lethal. Failure can be instructive and even fun! (Even, dare I say it, . . . "character building"?) Honor is so important in that setting that a moment of lost honor, a recognition that they aren't perfect in all things, can do wonders in terms of future character motivation. Plan for the characters to fail.
That is not to say that they should never succeed or not learn anything, though, but there are ways of doing that without having direct social-roll confrontations or even after failing at all direct confrontations.
First, don't worry about giving them a loyal subordinate with the social skills to take on the courtiers some of the time, and don't worry about fudging the rolls for him up or down if you have to . . . maybe he's talented but new and prone to rookie mistakes or getting rather old and not as fast or perceptive as he used to be. Also, don't worry about having him advise the PCs. However, his advice shouldn't just be "do this"; have him offer multiple options with pros and cons and let things play out from there. Heck, let him be wrong sometimes just so the PCs don't rely on him too heavily. (A sufficiently deep intrigue will have elements he couldn't expect, or that were expecting him. . . .)
Second, give them plots where their bumbling or social weaknesses are strengths. Have enemies overestimate them and plan for the wrong reaction from the PCs, have their bumbling somehow convince everyone that they know more than they do (spooking the enemy into making mistakes), have them accidentally round up all the right people for all the wrong reasons and someone confesses to the plot and then asks how they knew, or just plain have things come to a point where the villains are expecting some nuanced social reaction they can parry and the heroes decide to just charge in and take care of things the old-fashioned way.
There's one more option: The overestimated idiot at the center of a backstabbing circle. In social politics, this is where everyone tries to curry favor with the lord by telling on everyone else. As a result, the lord is spectacularly well-informed about everyone else's secrets and develops a reputation for being an omnicient badass when all they had to do was sit there and look stern and knowing. If your players can handle that kind of information effectively, they'll find ways of taking care of business without ever having to make a social roll they don't like.
Best Answer
If you can get them to read novels in the setting, that's ideal. But it may take some time and I've never met a full group that would all read the same books, even when bribed with XP.
Here's more of a quick and dirty method. A few games ago I gave the players cheat sheets about the city they were in. I limited them to a page each because the more I give them to read, the less they retain. However, I made sure to give the group different cheat sheets. This let me distribute more than a single page of material to them and it let them look smart when they told the group about things their characters should know about. Oh and I made sure to include a few differences of opinion on similar items in the cheat sheet, just to get the players arguing.
That said, that particular game was isolated to a single city. A game with travel would probably need more than a single sheet. I think you could get away with this method if you gave out info as needed, rather than all at once. Your players won't want to read 10 pages of notes before the game even begins, but if you give them each a page whenever they enter a new country, they should be able to handle that.